[style-guide] prefer leading rather than trailing operators

This is a suggestion regarding position of operators in chained expressions

starting from:

```fsharp
if
long-thing &&
another-long-thing &&
another-long-thing &&
another-long-thing
then
```

I generally feel it is actually better (especially with long things) to put the operator in a leading position on the next line:

```fsharp
if
long-thing
&& another-long-thing
&& another-long-thing
&& another-long-thing
then
```

The same rule could be extended for `,` as well.

```fsharp
let a =
long-thing,
another-long-thing,
another-long-thing
```

```fsharp
let a =
long-thing
, another-long-thing
, another-long-thing
```

Note that F# users tend to use `|>` operator in such manner.

Also, most languages using "fluent notation" (chaining method calls), would put the `.` operator in leading position of next line

```fsharp
a
.Something()
.AnotherThing()
```

I've consistently felt it is more readable, easier to extend code, in many languages, using this type of positioning.